The replacement of asbestos in conventional friction products is desirable because of the suspected health and safety hazards linked to the human contact of asbestos. Various approaches to the replacement of asbestos in friction products have led to a substantial body of art that has been categorized into three groups of non-asbestos type formulations. They are: (1) semi-metallic formulations; (2) organic non-asbestos formulations; and (3) cold molding hydrocarbon formulations. Such categories are generally illustrated in U.S. Pat. Nos. 3,856,120; 4,137,214; and 4,125,496, respectively. Additional examples of these non-asbestos formulations may be found in U.S. Pat. Nos. 4,278,584; 4,226,758; 4,226,759; and 4,219,452.
The elimination of asbestos from friction material formulations has created a substantial manufacturing problem. In conventional friction product manufacture, the components of the friction product are typically mixed, formed into a preform (or "green mold") at ambient temperatures, and then subjected to simultaneous pressure and heat curing, and finally to oven curing thereby obtaining the final friction product. Asbestos-based formulations, when in the preform stage, have sufficient structural integrity to withstand normal handling and storage prior to the hot molding process. But non-asbestos formulations do not possess acceptable structural integrity so as to be able to withstand subsequent handling and storage without breakage.
U.S. Pat. Nos. 4,374,211 and 4,866,107 are directed to the solution of the above problem, that is increasing the structural integrity of non-asbestos friction product formulation preforms. In U.S. Pat. No. 4,374,211, the structural integrity of the preforms is increased by the addition of an aramid polymer in the form of a pulp fiber. In U.S. Pat. No. 4,866,107, the same result is obtained by the use of a fibrillated acrylic polymer fiber.